Rigid polyurethane foams and processes for their production are well known in the art. Such foams are typically produced by reacting a polyisocyanate with an isocyanate-reactive material such as a polyol in the presence of a chlorofluorocarbon blowing agent. It is also known, however, that these chlorofluorocarbon blowing agents pose environmental problems.
Alternatives to the known chlorofluorocarbon blowing agents are currently the subject of much research. Hydrogen chlorofluorocarbons (HCFC) are among the most promising alternatives. However, some HCFCs must be used in larger amounts than the traditional chlorofluorocarbons and often result in foams having thinner cell walls. The HCFCs also tend to migrate from foam cell cavities thereby reducing the insulation value of the foam. Further, HCFCs produce a more thermally conductive foam insulation which reduces the energy efficiency of appliances, e.g., which are insulated with such foams. Consequently, substitution of HCFCs for the traditional chlorofluorocarbons may resolve the environmental problems created by chloro-fluorocarbons but it creates an energy efficiency problem.
Dichlorofluoroethane ("HCFC-141b") has been described as being useful as a blowing agent for rigid isocyanate-based foams (see U.S. Pat. No. 5,254,601). Perfluorinated aliphatic hydrocarbons, perfluorinated cycloaliphatic hydrocarbons and perfluorinated ethers have also been described as being useful as blowing agents for rigid isocyanate-based foams alone and in combination with other blowing agents (U.S. Pat. Nos. 4,972,002 and 5,034,424). Perfluorinated N-aliphatic, cyclic 1,3- and 1,4aminoethers (U.S. Pat. No. 5,162,384) and perfluorinated tertiary alkylamines (U.S. Pat. No. 5,187,206) are also described as being useful as blowing agents alone and in combination with other blowing agents. Finally, perfluorinated hydrocarbons have been described as being useful in improving the insulating capacity of foams (U.S. Pat. No. 4,981,879).
It has also been suggested that carbon black can improve the thermal insulating properties of rigid isocyanate-based foams (see U.S. Pat. Nos. 4,795,763 and 5,137,930).